After I race..I sometimes sneeze non stop. I thought it was due to allergies..but I sneezed out of control today after an indoor 5k. It does not always happen....does anyone else have this. What can be the causes?

Well, sneezing is usually due to airborne particles inhabiting your nostrils, and it's your body's way of getting them out. If you can truly isolate the precaution that allergies are the problem, then you can assume that all the inhaling probably shoved a bunch of dust particles into your nose.